Glaucoma treatment

ABSTRACT

Elevated glutamate levels are associated with glaucoma, and damage to retinal ganglion cells can be controlled by administering to the patient a compound capable of reducing glutamate induced excitotoxicity in a concentration effective to cause reduction of such excitotoxicity.

This application relates to glaucoma treatment.

BACKGROUND OF THE INVENTION

Glaucoma affects approximately five percent of persons who are older than 65 years and fourteen percent of those older than 80 years. The visual loss which results from glaucoma conditions has been attributed to progressive damage of the optic nerve and consequent loss of retinal ganglion cells, mediated by elevated intraocular pressure (Quigley et al., Invest. Ophthalmol. Vis. Sci. 19:505, 1980). Consequently, therapeutic modalities have focused on the management of intraocular pressure.

Many compounds have been proposed to treat glaucoma. See generally, Horlington U.S. Pat. No. 4,425,346; Komuro et al. U.S. Pat. No. 4,396,625; Gubin et al. U.S. Pat. No. 5,017,579; Yamamori et al. U.S. Pat. No. 4,396,625; and Bodor et al. U.S. Pat. No. 4,158,005.

At the present time, medical control of intraocular pressure consists of topical or oral administration of a miotic (e.g., pilocarpine), epinephrine derivatives (e.g., dipivalyl epinephrine), or topical beta blockers (e.g., timolol). Abelson U.S. Pat. No. 4,981,871 discloses the use of a class I voltage-dependent Ca⁺⁺ channel blocking agent (a phenylalkylamine) to treat elevated ocular pressure (Specifically, Abelson '871 discloses the use of verapamil, which does not cross the blood brain barrier and does not reach retinal ganglion cells).

Miotics may reduce the patient's visual acuity, particularly in the presence of lenticular opacities. Topical beta blockers such as Timolol™ have been associated with systemic side effects such as fatigue, confusion, or asthma, and exacerbation of cardiac symptoms has been reported after rapid withdrawal of topical beta blockers. Oral administration of carbonic anhydrase inhibitors, such as acetazolamide, may also be used, but these agents can be associated with systemic side effects including chronic metabolic acidosis.

If current methods of treatment fail to reduce intraocular pressure, laser treatment or a drainage operation (e.g., trabeculectomy) is usually performed.

SUMMARY OF THE INVENTION

We have discovered that glaucoma is associated with elevated glutamate. We have further discovered that glaucoma management, particularly protection of retinal ganglion cells, can be achieved by administering to the patient a compound capable of reducing glutamate-induced excitotoxicity in a concentration effective to reduce such excitotoxicity, thereby reducing the loss of retinal ganglion cells resulting from such excitotoxicity.

By way of additional background underlying the invention, excessive influx of Ca²⁺ due to glutamate-mediated receptor activation is thought to underlie excitotoxicity. Several types of calcium-permeable ion channels that can be involved in this excitotoxicity are mentioned below, including voltage-dependent Ca²⁺ channels, the NMDA receptor channel complex, and other channels directly coupled to glutamate (or excitatory amino acid) receptors. Such channels are reviewed in Sommer, B. and Seeburg, P. H. Glutamate receptor channels: novel properties and new clones. Trends Pharmacological Sciences 13:291-296 (1992); Nakanishi, S. Molecular Diversity of glutamate receptors and implications for brain function. Science 248:597-603 (1992).

One aspect of the invention generally features administering antagonists of glutamate-induced excitotoxicity that are capable of crossing both the blood-brain barrier and the blood-retina barrier to human patients with non-vascular glaucoma--i.e., all types of glaucoma other than the type commonly termed "neo-vascular" glaucoma.

A second aspect of the invention features the use of antagonists that do not have a substantial direct effect on glutamate toxicity mediated by the L-type voltage dependent Ca⁺⁺ channel, but instead affect glutamate toxicity mediated by other mechanisms detailed below. We consider that a compound has a substantial direct effect on glutamate toxicity mediated by the L-type voltage dependent Ca⁺⁺ channel if it produces a statistically significant result in experiments measuring glutamate induced effects by the general method described in Karschian and Lipton, J. Physiol. 418: 379-396 (1989) or by other techniques for measuring antagonism of the L-type Ca⁺⁺ channel known to those in the art. (We contrast the direct effect so measured with the secondary effects of excitoxicity mediated by other channels, which in turn causes flow through the voltage dependent Ca⁺⁺ channels.) In particular, this aspect of the invention features use of compounds which are not Class I voltage dependent Ca⁺⁺ channel antagonists, e.g., compounds-that are not phenylalkylamines. Preferably, this second aspect of the invention features antagonists of the N-methyl-D-aspartate (NMDA) receptor channel complex and other glutamate receptor antagonists described in detail below. Other useful compounds according to the invention include antagonists of non-NMDA receptors--i.e. antagonists of glutamate induced excitotoxicity that do substantially affect excitotoxicity mediated via the NMDA receptor channel complex (e.g., excitoxicity caused by NMDA in experiments well known to those in the art), but instead operate by antagonizing excitoxicity mediated via other glutamate receptors. Also, antagonists of the second aspect are used in preferred embodiments of the first aspect of the invention.

According to both aspects, the invention preferably will be used to treat patients which have primary open-angle glaucoma, chronic closed-angle glaucoma, pseudoexfoliation, or other sub-types of glaucoma or ocular hypertension. Preferably, the agent is administered over an extended period (e.g., at least six months and preferably at least one year), regardless of changes in the patient's intraocular pressure over the period of administration.

Particularly preferred compounds used in both aspects of the invention are antagonists of the NMDA receptor-channel complex. The term "NMDA receptor antagonists" includes several sub-types of NMDA antagonists including: a) channel blockers--i.e., antagonists that operate uncompetitively to block the NMDA receptor channel; b) receptor antagonists--antagonists that compete with NMDA to act at the NMDA binding site; c) agents acting at either the glycine co-agonist site or any of several modulation sites such as the zinc site, the magnesium site, the redox modulatory site, or the polyamine site; d) agents which inhibit the downstream effects of NMDA receptor stimulation, such as agents that inhibit activation of protein kinase C activation by NMDA stimulation, antioxidants, and agents that decrease phosphatidylinositol metabolism.

Other compounds that are useful in the invention include voltage-dependent calcium channel antagonists which are described in greater detail below, particularly those which cross the blood-brain and blood-retina barriers and which can be administered chronically. Other preferred agents act as antagonists of non-NMDA receptors (glutamate receptor types other than the NMDA receptor complex discussed above), and include agents which block ionotropic glutamate receptors or interact with metabotropic glutamate receptors (Nakanishi, supra). Other preferred agents act to limit (reduce) release of glutamate from cells, thereby acting upstream from the glutamate receptors in the excitatory neurotoxicity process. Still other agents may act by blocking downstream effects of glutamate receptor stimulation, e.g., the intracellular consequences of glutamate interaction with a cell membrane glutamate receptor, such as agents (like dantrolene) that block the rise in intracellular calcium following stimulation of membrane glutamate receptors.

The most preferred compounds are those capable of crossing the blood-brain barrier or the blood-retinal barrier; these compounds may be administered orally, intravenously, or topically and cross intervening barriers including the blood brain barrier to reach the retinal ganglion cells. Compounds that do not freely cross the blood-brain barrier are less preferred; these compounds may be administered intravitreally to the retina. In the case of compounds that have an intermediate ability to cross the blood-brain barrier, the mode of administration will depend on the dosage required and other factors.

Among the preferred compounds are amantadine derivatives (e.g., memantine, amantadine, and rimantadine), nitroglycerin, dextorphan, dextromethorphan, and CGS-19755. See generally, the compounds listed in Table 2.

The invention is useful for the reduction or prevention (including prophylactic treatment) of damage to retinal ganglion cells and their axons comprising the optic nerve in patients with glaucoma.

Other features and advantages of the invention will be apparent from the following description of the preferred embodiment thereof, and from the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawings will first be briefly described. Drawings

FIG. 1 is a bar graph of normalized amino acid concentrations in glaucomatous vitreous when compared to control vitreous.

FIG. 2 is a graph of amino acid concentration of glutamate in vitreous plotted as a function of years of glaucoma.

Following is a detailed description indicating that increased levels of glutamate in the vitreous is associated with glaucoma mediated damage of the optic nerve. We do not wish to bind ourselves to a specific theory. However, in view of well documented literature establishing the excitotoxic effect of glutamate on neurons of the central nervous systems, including retinal neurons, it is likely that the compounds of the invention are useful for treating glaucoma because of their ability to block glutamate induced excitoxicity. Also outlined are assays which provide one skilled in the art with the necessary guidance to determine the potential efficacy of receptor antagonists in reducing or preventing damage of the retinal ganglion cells.

Detection of Vitreal Levels of Glutamate

Vitreous samples from twenty-six glaucomatous and non-glaucomatous patients (on the General Eye and Glaucoma Consultation Services of the Massachusetts Eye and Ear Infirmary) were assayed. Samples were centrifuged at high speed in a Microfuge for 60 minutes at 4° C. The supernatant was then immediately frozen in liquid nitrogen and stored at -80° C. until assayed for amino acid concentration. Amino acid analyses were performed by the Neurochemistry Laboratory of the Massachusetts General Hospital. Immediately before analysis, salicylic acid was added to each sample. Analyses were carried out by cation exchange on a Beckmann Amino Acid Analyzer (model 6300), as described in detail previously (Lipton, et al. Neuron, 7:11, 1991). Duplicate analyses of samples from three controls with cataract and three patients with glaucoma were performed by the Amino Acid Laboratory at Children's Hospital of Boston. These duplicate values agreed in all cases within 9% of the results obtained at the Massachusetts General Hospital laboratory.

Samples were obtained from fifteen patients with documented glaucoma and cataract, and from eleven patients with cataract alone. Each patient with glaucoma (either primary open angle, chronic angle closure, or pseudoexfoliation) had either been on anti-glaucoma therapy for at least one year prior to cataract surgery, or had undergone a filtering operation for pressure control.

Amino acid analyses reveal an approximately two-fold elevation in glutamic acid levels in patients with glaucoma and cataract when compared to cataractous controls (FIG. 1 and Table 1). Data were analyzed by the students' t test and were significant at p<0.0001. Apart from glutamate, no other statistically significant variation in amino acid concentrations was detected in these patients. The data were further stratified by patient age, axial length of the eye, sex, race, type or severity of cataract (as judged preoperatively), etiology of glaucoma, or type of anti-glaucoma therapy. The presence and severity of cataract (based upon pre-operative examination and cataract type) were similar between the control and glaucoma groups. Thus the group of patients with cataract alone could serve as an appropriate control group.

                  TABLE 1     ______________________________________     Amino Acid Concentrations in Vitreous of     Control and Glaucoma Patients     Amino Acid:* Controls:   Glaucoma:     ______________________________________     Alanine      167.4 ± 44.3                              159.1 ± 50.7     Aspartate    Not Detectable†                              Not Detectable.sup.†     Glutamic Acid                  12.6 ± 1.8                               22.3 ± 2.8.sup.‡     Glutamine    479.0 ± 33.1                              466.1 ± 41.1     Glycine      22.9 ± 5.0                               27.6 ± 22.9     Histidine    34.2 ± 3.7                              32.5 ± 3.3     Isoleucine   35.1 ± 1.2                              34.1 ± 4.4     Leucine      77.9 ± 2.5                              73.6 ± 7.9     Lysine       106.3 ± 4.6                              101.5 ± 7.7     Methionine   21.5 ± 2.2                              20.1 ± 2.9     Phenylalanine                  63.4 ± 4.7                              58.9 ± 6.9     Serine       105.5 ± 8.7                              98.6 ± 7.6     Threonine    57.5 ± 6.5                              56.8 ± 7.3     Tyrosine     15.8 ± 1.3                              15.6 ± 1.2     Valine       143.6 ± 19.1                              143.2 ± 19.4     ______________________________________      .sup.(*.sup.) All concentrations are μmols/liter ± standard      deviation; those amino acids not tabulated were not analyzed.      .sup.(†) Below 5 μmols/liter.      .sup.(‡) When compared to control, significant by the students      t test at P < 0.0001.

The glutamate concentrations detected in these patients were also plotted as a function of time from the diagnosed onset of the disease with patients having cataract alone plotted at time zero. A graph of these data is shown in FIG. 2. The correlation coefficient for the line drawn is r=0.702. Thus, although elevated in all glaucomatous vitreous assayed, there is a direct correlation between the level of glutamate and the stage of visual loss from glaucoma.

The elevated glutamate can damage neurons by NMDA-mediated activation; and glutamate (or congener) activation of non-NMDA receptors could also contribute to retinal ganglion cell loss, and may be important to control, even if the NMDA contribution predominates. See, generally, Sucher et al. J. Neurosci.,11:966 (1991).

One explanation for the toxic level of glutamate found in glaucomatous vitreous is that it is released by dying cells during the course of the destruction occasioned by the glaucomatous process. For example, other forms of trauma to nerve cells are known to lead to the accumulation of extracellular glutamate (Faden et al. Science, 244:798-800 (1989)), and the elevated pressure of the glaucomatous process could exert traumatic injury on cells. The glutamate thereby released could, in turn, lead directly to further neuronal injury. A second possibility is that the glaucomatous process (perhaps through elevated pressure on the cell soma) leads to increased permeability of damaged retinal cells, exposing intracellular stores of glutaminase. This might promote the conversion of glutamine to glutamate. However, whatever the mechanism of generation, this neurotoxin is elevated in the glaucomatous population, and therefore participates in the destruction of retinal ganglion cells and the consequent visSel loss seen in this disease.

Selection of Antagonists

In view of our discovery that such excitotoxicity is associated with glaucoma, the invention features antagonists having certain specific characteristics: the ability to cross the blood-brain and blood-retina barriers; and the ability to be administered chronically, even when intraocular pressure has been controlled to within normal ranges. Within those guidelines, any suitable antagonist of the glutamate induced exitotoxicity may be used in accordance with the invention. As mentioned, in preferred embodiments, N-methyl-D-aspartate (NMDA) subtype of glutamate receptor-channel complex may be used to reduce or prevent glaucoma related injury to the retinal ganglion cells and their axons comprising the optic nerve with consequent vision loss. Many antagonists of the NMDA receptor have been identified (Watkins et al., Trends in Pharmacological Sci. 11:25, 1990, hereby incorporated by reference). There are several recognized sub-types of NMDA receptor including: a) channel blockers--i.e., antagonists that operate non-competitively to block the NMDA receptor channel; b) receptor antagonists--antagonists that compete with NMDA, acting at the NMDA binding site; c) agents acting at either the glycine co-agonist site or any of several modulation sites such as the zinc site, the magnesium site, the redox modulatory site, or the polyamine site; d) agents which inhibit the downstream effects of NMDA receptor stimulation such as agents that inhibit activation of protein kinase C activation by NMDA stimulation, antioxidants, and agents that decrease phosphatidylinositol metabolism.

Other compounds that are useful in this invention include: other non-NMDA receptor antagonists, such as agents which block other types of ionotropic glutamate receptors or interact with metabotropic glutamate receptors; voltage-dependent calcium channel antagonists (against L, N, T, and P type channels) (Bean, B.P. Annu. Rev. Physiol. 51:367-384 (1989); Hess, P. Annu. Rev. Neurosci. 13:337-356 (1990)), and are described in greater detail below; and agents which act to decrease the release of glutamate, thereby acting upstream in the excitatory neurotoxicity process.

Table 2, below lists various suitable NMDA and non-NMDA receptors which do not operate via the voltage-dependent Ca⁺⁺ ion channel. Tables 3-5 list antagonists of the voltage dependent Ca⁺⁺ channel, which can be used by themselves in connection with the first aspect of the invention, and which can also be used in combination with other antagonists in the second aspect of the invention.

                                      TABLE 2     __________________________________________________________________________     NMDA Antagonists    NMDA Antagonists     NMDA Antagonists     __________________________________________________________________________     1. Competitive NMDA Antagonists (act                         2. Channel Blockers (Un-Competitive                                              3. Antagonists at Glycine Site                                              of the     at agonist binding site)                         NMDA Antagonists)    NMDA Receptor     CGS-19755 (CIBA-GEIGY) and other                         MK-801 (Dizocilpine) and other                                              Kynurenate, 7-chloro-kynurenate,                                              5,7-     piperdine derivatives, D-2-amino-5-                         derivatives of dibenzyocycloheptene                                              chloro-kynurenate,                                              thio-derivatives, and     phosphovalerate, D-2-amino-7-                         (Merck)              other derivatives. (Merck)     phosphonoheptanoate (AP7)     CPP{ 3-(2-carboxypiperazin-4-y-propyl-                         Sigma receptor ligands, e.g. Dextrorphan,                                              Indole-2-carboxylic acid     1-phosphonic acid!} dextromethorphan and morphinan                         derivatives (Hoffman La Roche) such as                         caramiphen and rimcazole (which also                         block calcium channels)     LY 274614, CGP39551, CGP37849,                         Ketamine, Tiletamine and other                                              DNQX     LY233053, LY233536  cyclohexanes     O-phosphohomoserine Phencyclidine (PCP) and derivatives,                                              Quinoxaline or oxidiazole                                              derivatives                         pyrazine compounds   including CNQX, NBQX     MDL 100, 453        Memantine, amantadine, rimantadine and                                              Glycine partial agonist (e.g.                                              Hoecht-                         derivatives          Roussel P-9939)                         CNS 1102 (and related bi- and tri-                         substituted guanidines)                         Diamines                         Conantokan peptide from Conus                         geographus                         Agatoxin-489     __________________________________________________________________________     NMDA Antagonists    NMDA Antagonists     NMDA Antagonists     __________________________________________________________________________     4. Polyamine Site of NMDA Receptor                         5. Redox Site of NMDA Receptor                                              6. Other Non-Competitive NMDA                                              Antagonists     Arcaine and related biguanidines and                         Oxidized and reduced glutathione                                              Hoechst 831917189     biogenic polyamines     Ifenprodil and related drugs                         PQQ (pyrroloquioline quinone)                                              SKB Carvedilol     Diethylenetriamine SL 82,0715                         Compounds that generate Nitric Oxide (NO)                         or other oxidation states of nitrogen monoxide                         (NO+, NO-) including those listed in the box                         below     1,10-diaminodecane(and related inverse                         Nitroglycerin and derivatives, Sodium     agonists)           Nitroprusside, and other NO generating listed                         on p. 5 of this table                         Nitric oxide synthase (NOS) Inhibitors                         Arginine analogs including N -mono-methyl-                         L-arginine (NMA); N -amino-L-arginine                         (NAA), N -nitro-L-arginine (NNA); N -                         nitro-L-arginine methyl ester; N-iminoethyl-                         L-ornithine                         Flavin Inhibitors: diphenyliodinium;                         Calmodulin inhibitors, trifluoperizine                         Calcineurin Inhibitors, e.g., FK-506 (inhibits                         calcineurin and thus NOS diphosphorylase)     __________________________________________________________________________     Inhibitors of Downstream                         Inhibitors of Downstream                                              Non-NMDA Receptor     Effects of NMDA     Effects of NMDA      Antagonists     __________________________________________________________________________     7. Agents to inhibit protein kinase C                         8. Downstream effects from Receptor                                              9A. Non-NMDA antagonists     activation by NMDA stimulation                         Activation           (Competitive)     (involved in NMDA toxicity)     MDL 27,266 (Merrill Dow) and triazole-                         8a. To decrease phopshatidylinositol                                              CNQX, NBQX, YM900, DNQX,     one derivatives     metabolism           PD140532     Monosialogangliosides (eg GM1 of Fidia                         kappa opioid receptor agonist:                                              AMOA (2-amino-3 3-9carboxymethoxy                                              l-     Corp.) and other ganglioside derivatives                         U50488(Upjohn) and dynorphan                                              5-methoxylisoxazol-4-yl!propionat                                              e!     LIG20, LIGA4 (may also effect calcium     extrusion via calcium ATPase)                         kappa opioid receptor agonist: PD117302,                                              2-phosphophonoethyl                                              phenylalanine                         CI-977               derivatives, i.e. 5-ethyl,                                              5-methyl, 5-                                              trifluoromethyl                         8b. To decrease hydrogen peroxide and                         free radical injury, eg antioxidants                         21-amino steroid (lazaroids) such as                                              9B. Non-NMDA Non competitive                         U74500A, U75412E and U7400F                                              antagonists                         U74389F, FLE26749, Trolox (water                                              GYKI52466                         soluble alpha tocophenol), 3,5-dialkoxy-4-                         hydroxy-benzylamines                         Compounds that generate Nitric Oxide                                              Evans Blue                         (NO) or other oxidation states of nitrogen                         monoxide (NO+, NO-) including those                         listed in the box below                         Nitroglycerin and derivatives, Sodium                         Nitroprusside, and other NO generating                         listed on p. 5 of this table                         Nitric oxide synthase (NOS) Inhibitors:                         Arginine analogs including N -mono-                         methyl-L-arginine (NMA): N -amino-L-                         arginine (NAA); N -nitro-L-arginine                         (NNA); N -nitro-L-arginine methyl ester;                         N-iminoethyl-L-ornithine     __________________________________________________________________________     Agents Active at                         Drugs to decrease intracellular     Metabotropic Glutamate                   calcium following glutamate     Receptors           Decrease glutamate release                                              receptor stimulation     __________________________________________________________________________     10a. Blockers of Metabotropic                         11. Agents to decrease glutamate release                                              12a. Agents to decrease                                              intracellular caclium     Glutamate Receptors                      release     AP3 (2-amino-3-phosphonoprionic acid)                         Adenosine, and derivatives, e.g.                                              Dantrolene (sodium dantrium);                                              Ryanodine (or                         cyclohexyladenosine  ryanodine + caffiene)     10b. Agonsts of Metabotropic                         CNS1145              12b. Agents inhibiting                                              intracellular Calcium-     Glutamate Receptors                      ATPase     (1S,3R)-1-Amino-cyclopentane-1,3-                         Conopeptides: SNX-111, SNX-183, SNX-                                              Thapsigargin, cyclopiazonic                                              acid, BHQ ( 2,5-     dicarboxylic acid  (1S,3R-ACPD!,                         230                  di-(tert butyl)-1,4-benzohydroqui                                              none; 2,5-di-     commonly ref as `trans`-ACPD             (tert-butyl)-1,4benzohydroquinone                                              !)                         Omega-Aga-IVA, toxin from venom of                         funnel web spider                         Compounds that generate Nitric Oxide                         (NO) or other oxidation states of nitrogen                         monoxide (NO+, NO-) including those                         listed in the box below                         Nitroglycerin and derivatives, Sodium                         Nitroprusside, and other NO generating                         listed on p. 5 of this table                         Nitric oxide synthase (NOS) Inhibitors:                         Arginine analogs including N -mono-                         methyl-L-arginine (NMA); N -amino-L-                         arginine (NAA); N -nitro-L-arginine                         (NNA), N -nitro-L-arginine methyl ester;                         N-iminoethyl-L-ornithine     __________________________________________________________________________     Additional NO-generating     compounds     __________________________________________________________________________     Isosorbide     dinitrate (isordil)     S-nitrosocaptopril     (SnoCap)     Serum albumin coupled to     nitric oxide (SA-NO)     Cathepsin coupled to nitric     oxide (cathepsin-NO)     Tissue plasminogen     activator coupled to     NO (TPA-NO)     SIN-1 (also known as     SIN1 or molsidomine)     Ion-nitrosyl complexes (e.g.,     nitrosyl-iron complexes,     with iron in the Fe2+ state)     Nicorandil     __________________________________________________________________________

                  TABLE 3     ______________________________________     Antagonists of the Voltage Dependent Calcium Channels (N, L.     T, P and other types)     ______________________________________     dihydropyridines (e.g., nimodipine)     phenylalkylamines (e.g., verapamil, (S)-emopamil, D-600, D-     888)     benzothiazepines (e.g., diltiazem and others)     bepridil and related drugs     diphenylbutylpiperdines     diphenylpiperazines (e.g., flunarizine/cinnarizine series)     HOE 166 and related drugs     fluspirilene and related drugs     toxins and natural compounds (e.g., snail toxins -      ωconotoxin GVIA and GVIIA, maitotoxin, taicatoxin,      tetrandine, hololena toxin, plectreurys toxin,      funnel-web spider venom and its toxin fraction,      agatoxins including ω-agatoxin IIIA and ω-agatoxin      IVA.     ______________________________________

                  TABLE 4     ______________________________________     DIHYDROPYRIDINE CALCIUM CHANNEL ANTAGONISTS     ______________________________________     nifedipine         KW3049     niludipine         oxodipine     PY108-068 (darodipine)                        CD349     mesudipine         TC81     GX 1048            YM-09730-5 or (4S)DHP     floridine          MDL72567     nitrendipine       Rol8-3981     nisoldipine        DHP-218     nimodipine         nilvadipine     nicardipine        amlodipine     felodipine         8363-S     PN200-110 (Isradipine)                        iodipine     CV4093             azidopine     ______________________________________

                  TABLE 5     ______________________________________     OTHER CALCIUM CHANNEL ANTAGONISTS     ______________________________________     diclofurime        D-600     pimozide           D-888     prenylamine        Smith Kline 9512     fendiline          ranolzine     perhexiline        lidoflazine     mioflazine         CERM-11956     flunarizine/cinnarizine                        R-58735      series            R-56865     verapamil          amiloride     dilfiazine         phenytoin     dipropervine       thioridazine     (S)-emopamil       tricyclic antidepressents     ______________________________________

In Vitro Neuronal Cell Death Assay

An antagonist may be tested for utility in the method of the invention by monitoring neuronal cell death in retinal ganglion cells incubated in vitro with glutamate. The ability of the antagonist to reduce neuronal cell death is determined by scoring live cells which have been incubated overnight with both glutamate and the drug.

Retinal ganglion cells from postnatal rats are identified and their viability ascertained as follows. Under general anesthesia, the fluorescent dye granular blue (Mackromolekulare Chemic, Umstadt, FRG) is injected as approximately a 2% (w/v) suspension in saline into the superior colliculus of 4- to 7-day-old Long Evans rats (Charles River Laboratory, Wilmington, Mass.). Two to 7 days later, the animals are killed by decapitation and enucleated, and the retinas quickly removed. The retinas are then dissociated and cultured in Eagle's minimum essential medium (MEM, catalog #1090, Gibco Grand Island, N.Y.), supplemented with 0.7% (w/v) methylcellulose, 2 mM glutamine, 1 μg/ml gentamicin, 16mM dextrose, and 5%(v/v) rat serum, as described in Lipton et al., J. Physiol., 385:361, (1987) (except that when using a Ca⁺⁺ ! of 3mM or higher--the level found in the vitreous--Mg⁺⁺ was omitted to enhance NMDA receptor-mediated neurotoxicity--see, Levy et al. Neurology, 40:852-855 (1990); Hahn et al. Proc. Nat'l Acad. Sci. USA, 85:6556-6560 (1988). The cells are plated onto 75 mm² glass coverslips coated with poly-L-lysine in 35 mm tissue culture dishes; glutamate is then added. Sibling cultures receive various doses of NMDA receptor-channel complex antagonists, or non-NMDA antagonists with and without glutamate (e. g., 25 μM).

Cell survival is assayed after one day in culture at 37° C. in an atmosphere of 5% CO₂ /95% air. Ganglion cells can be unequivocally identified by the continued presence of the fluorescent blue dye. The ability of retinal ganglion cells to take up and cleave fluorescein diacetate to fluorescein is used as an index of their viability as described in detail in Hahn et al., supra. Dye uptake and cleavage correlates well with normal electrophysiological properties assayed with patch electrodes.

To perform the viability test, the cell-culture medium is exchanged for physiological saline containing 0.0005% fluorescein diacetate for 15-45 s, and then cells are rinsed in saline. Retinal ganglion cells that do not contain the fluorescein dye (and thus are not living) often remain visible under both phase-contrast and UV fluorescence optics, the latter because of the continued presence of the marker dye granular blue; other dead retinal ganglion cells disintegrate and only debris remains. In contrast, the viable retinal ganglion cells display not only a blue color in the UV light but also a yellow-green fluorescence with filters appropriate for fluorescein. Thus, the use of two exchangeable fluorescence filter sets permits the rapid determination of the number of viable ganglion cells in the cultures, which are found as solitary neurons or lying among other cells in small clusters (usually in the ratio of approximately 1:10 solitary to clustered). Statistical analyses consisting of a one-way analysis of variance followed by a Scheffe multiple comparison of means is then conducted to determine the effectiveness of drugs such as the NMDA antagonists and/or non-NMDA antagonists in preventing glutamate excitotoxicity.

Use

An effective receptor antagonist will cause a decrease in glaucoma-associated retinal ganglion cell damage or death. As described above, the preferred compounds which cross the blood-brain and blood retinal barriers are preferably administered topically or orally in known, physiologically acceptable vehicles including tablets, liquid excipients and suspensions. Those skilled in the art will appreciate how to formulate acceptable therapeutics.

Antagonists may be compounded into a pharmaceutical preparation, using pharmaceutical compounds well-known in the art; the exact formulation and dosage of the antagonist compound depends upon the route of administration. Generally, the effective daily dose of the antagonists will range from 0.01 to 1000 mg/kg.

Other Embodiments

Other embodiments are within the following claims. For example, the method of the invention may be used for treatment of retinal ganglion cell damage associated with glaucoma in combination with other modes of treatment, e.g, those that are directed to reducing intraocular pressure such as those described herein. In the method of the invention, a useful compound may be administered by any means that allows the compound access to the retinal ganglion cells whose axons comprise the optic nerve. The compounds useful in the method include antagonists of excitatory amino acid receptors (both NMDA and non-NMDA subtypes) that act to reduce retinal ganglion cell neuronal injury via the glaucoma mediated rise in extracellular glutamate, or which reduce binding of glutamate to the NMDA receptor. The antagonists can act to prevent cell death by acting at a modulatory site or a co-agonist site, or by blocking the chain of events initiated by receptor activation.

Other embodiments are within the following claims. 

What is claimed is:
 1. A method of protecting against retinal damage in a human glaucoma patient, said method comprising administering to said patient a compound that is an uncompetitive antagonist of the NMDA receptor-channel complex in an amount effective to effect such protection, wherein said compound is an adamantane derivative.
 2. The method of claim 1 wherein said compound is capable of crossing the blood-brain barrier and the blood-retina barrier.
 3. The method of claim 1, wherein said glaucoma is chronic closed-angle glaucoma.
 4. The method of claim 1, wherein said glaucoma is primary open-angle glaucoma.
 5. The method of claim 1, wherein said glaucoma is pseudoexfoliation glaucoma.
 6. The method of claim 1, said compound being administered to said patient topically.
 7. The method of claim 1, said compound being administered to said patient orally.
 8. The method of claim 1, said compound being administered to said patient intravitreally.
 9. The method of claim 1 wherein said compound is administered chronically.
 10. The method of claim 1 comprising administering an adamantane derivative.
 11. The method of claim 1 comprising administering memantine, amantidine, or rimantidine.
 12. The method of claim 11 comprising administering memantine.
 13. A method of protecting a human patient from damage to retinal ganglion cells associated with non-vascular forms of glaucoma, said method comprising systemically or intravitreally administrating to said patient a compound that is an antagonist of glutamate induced excitotoxicity, in a concentration effective to cause reduction of said excitotoxicity, said antagonist being an antagonist of NMDA receptor-mediated neurotoxicity, wherein said compound is an adamantane derivative.
 14. A method of treating glaucoma in a human patient by administering to the retinal ganglion cells of a glaucoma patient a composition comprising an effective amount of an amantadine derivative that is an antagonist of NMDA receptor mediated neuronal toxicity.
 15. A method of treating glaucoma in a human patient by administering to the retinal ganglion cells of a glaucoma patient a composition comprising an effective amount of an compound selected from amantadine, rimantadine, and memantine.
 16. The method of claim 15 wherein the compound is memantine. 